$ afconvert -f mp4f -o birdland.mp4
$ afinfo birdland.mp4
File: birdland.mp4
File type ID: mp4f
Num Tracks: 1
----
Data format: 2 ch, 44100 Hz, 'aac ' (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame
no channel layout.
estimated duration: 12.240317 sec
audio bytes: 200206
audio packets: 530
bit rate: 130145 bits per second
packet size upper bound: 682
maximum packet size: 682
audio data file offset: 4096
optimized
audio 539798 valid frames + 2112 priming + 810 remainder = 542720
format list:
[ 0] format: 2 ch, 44100 Hz, 'aac ' (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame
Channel layout: Stereo (L R)
----
$ afconvert -f WAVE -d LEI16 birdland.mp4 birdland_aac.wav
$ afinfo birdland_aac.wav
File: birdland_aac.wav
File type ID: WAVE
Num Tracks: 1
----
Data format: 2 ch, 44100 Hz, 'lpcm' (0x0000000C) 16-bit little-endian signed integer
no channel layout.
estimated duration: 12.240317 sec
audio bytes: 2159192
audio packets: 539798
bit rate: 1411200 bits per second
packet size upper bound: 4
maximum packet size: 4
audio data file offset: 4096
optimized
source bit depth: I16
----